The present invention relates to the micron-scale alignment of components and in particular, the precise alignment of modular inkjet printheads manufactured using micro electro mechanical system (MEMS) techniques.
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention on May 24, 2000:
Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending application, PCT/AU00/01445, filed by the applicant or assignee of the present invention on Nov. 27, 2000. The disclosures of these co-pending applications are incorporated herein by cross-reference. Also incorporated by cross-reference, are the disclosures of two co-pending PCT applications filed Mar. 2, 2001, application numbers PCT/AU01/00216 and PCT/AU01/00217 (deriving priority from Australian Provisional Patent Application Nos. PQ5959 and PQ5957).
The present invention is particularly well suited to the assembly of CMOS (complementary metal oxide semiconductor) devices such as silicon computer chips. The invention will be described with particular reference to silicon printhead chips for digital inkjet printers wherein the nozzles, chambers and actuators of the chip are formed using MEMS techniques. However, it will be appreciated that this is in no way restrictive and the invention may also be used in many other applications.
Silicon printhead chips are well suited for use in pagewidth printers having stationary printheads. These printhead chips extend the width of a page instead of traversing back and forth across the page, thereby increasing printing speeds. The probability of a production defect in an eight inch long chip is much higher than a one inch chip. The high defect rate translates into relatively high production and operating costs.
To reduce the production and operating costs of pagewidth printers, the printhead may be made up of a series of separate printhead modules mounted adjacent one another, each module having its own printhead chip. To ensure that the printing produced is continuous across the width of the page, the chip in each module must be accurately aligned with the chips on adjacent modules. To assist with the alignment of adjacent chips, reference markings known as xe2x80x9cfiducialsxe2x80x9d are provided on each chip for optical alignment using a microscope.
The microscopic ink-nozzle structures are very fragile and may be damaged by unintentional contact. In situations requiring a certain level of robustness, the printhead chips have a protective guard to shield the ink nozzles. Unfortunately, the protective guard obscures the fiducials from the microscope.
According to a first aspect, the present invention provides a method of positioning a silicon chip, wherein the chip has a protective guard covering at least part of a surface of the chip, the method including:
providing at least one fiducial on the surface of the chip beneath the guard,
providing an aperture in the guard above the fiducial, the aperture being sized so as not to compromise effective protection provided by the guard; and,
viewing the fiducial through the aperture with a microscope to accurately position the chip.
Preferably, the chip is a MEMS inkjet printhead chip to be positioned so that its printing aligns with that of an adjacent printhead chip on an inkjet printer printhead. In a further preferred form, the printhead is a pagewidth printhead.
According to a second aspect, the present invention provides a silicon chip including:
a protective guard covering at least part of a surface of the chip;
a fiducial on the surface of the chip beneath the guard;
an aperture in the guard above the fiducial allowing it to be viewed by a microscope for the purpose of accurately positioning the chip; wherein,
the aperture is sized to accommodate the beam angle of the microscope without compromising the protection provided by the guard.
According to a third aspect, the present invention provides a method of accurately positioning a silicon chip wherein the chip has a protective guard covering at least part of a surface of the chip, the method including:
forming the guard from an infrared transparent material;
providing a fiducial on the surface of the chip beneath the guard for viewing with an infrared microscope to accurately position the chip.
According to another aspect, the present invention provides a silicon chip including:
a protective surface guard formed from an infrared transparent material;
a fiducial on the surface of the chip beneath the guard; wherein,
the fiducial is visible through the guard when viewed by an infrared microscope.
Preferably the infrared transparent material is silicon.
In one embodiment, the chip is a printhead chip for use in a pagewidth inkjet printer having a plurality of adjacent printhead chips.
It will be appreciated that using an appropriately sized aperture in the protective guard for forming the guard from a material that is transparent to the radiation sensed by the microscope, the present invention provides a convenient system for the precise alignment of silicon chips with guard structures without comprising the protection of the delicate nozzle structures on the chip surface.